5,461 research outputs found
Vegetation pattern formation in semiarid systems without facilitative mechanisms
Regular vegetation patterns in semiarid ecosystems are believed to arise from
the interplay between long-range competition and facilitation processes acting
at smaller distances. We show that, under rather general conditions, long-range
competition alone may be enough to shape these patterns. To this end we propose
a simple, general model for the dynamics of vegetation, which includes only
long-range competition between plants. Competition is introduced through a
nonlocal term, where the kernel function quantifies the intensity of the
interaction. We recover the full spectrum of spatial structures typical of
vegetation models that also account for facilitation in addition to
competition.Comment: 21 pages, 3 figure
Minimal mechanisms for vegetation patterns in semiarid regions
The minimal ecological requirements for formation of regular vegetation
patterns in semiarid systems have been recently questioned. Against the general
belief that a combination of facilitative and competitive interactions is
necessary, recent theoretical studies suggest that, under broad conditions,
nonlocal competition among plants alone may induce patterns. In this paper, we
review results along this line, presenting a series of models that yield
spatial patterns when finite-range competition is the only driving force. A
preliminary derivation of this type of model from a more detailed one that
considers water-biomass dynamics is also presented. Keywords: Vegetation
patterns, nonlocal interactionsComment: 8 pages, 4 figure
Online games: a novel approach to explore how partial information influences human random searches
Many natural processes rely on optimizing the success ratio of a search
process. We use an experimental setup consisting of a simple online game in
which players have to find a target hidden on a board, to investigate the how
the rounds are influenced by the detection of cues. We focus on the search
duration and the statistics of the trajectories traced on the board. The
experimental data are explained by a family of random-walk-based models and
probabilistic analytical approximations. If no initial information is given to
the players, the search is optimized for cues that cover an intermediate
spatial scale. In addition, initial information about the extension of the cues
results, in general, in faster searches. Finally, strategies used by informed
players turn into non-stationary processes in which the length of each
displacement evolves to show a well-defined characteristic scale that is not
found in non-informed searches.Comment: 17 pages, 10 figure
Spatial patterns in mesic savannas: the local facilitation limit and the role of demographic stochasticity
We propose a model equation for the dynamics of tree density in mesic
savannas. It considers long-range competition among trees and the effect of
fire acting as a local facilitation mechanism. Despite short-range facilitation
is taken to the local-range limit, the standard full spectrum of spatial
structures obtained in general vegetation models is recovered. Long-range
competition is thus the key ingredient for the development of patterns. The
long time coexistence between trees and grass, and how fires affect the
survival of trees as well as the maintenance of the patterns is studied. The
influence of demographic noise is analyzed. The stochastic system, under the
parameter constraints typical of mesic savannas, shows irregular patterns
characteristics of realistic situations. The coexistence of trees and grass
still remains at reasonable noise intensities.Comment: 12 pages, 7 figure
Soliton structures in a molecular chain model with saturation
In the present work, we study, by means of a one-dimensional lattice model,
the collective excitations corresponding to intra molecular ones of a chain
like proteins. It is shown that such excitations are described by the Nonlinear
Schrodinger equation with saturation. The solutions obtained here are the bell
solitons, bubbles, kinks and crowdons. Since they belong to different sectors
on the parametric space, the bubble condensation could give place to some
important changes of face in this kind of nonlinear system. Additionally, it is
shown that the limiting velocity of the solitons is the velocity of sound waves
corresponding to longitudinal vibrations of molecules.Comment: 12 pages, 4 figure
Effect of wood aging on wine mineral composition and 87Sr/86Sr isotopic ratio
The evolution of mineral composition and wine strontium isotopic ratio 87Sr/86Sr (Sr IR) during wood aging were
investigated. A red wine was aged in stainless steel tanks with French oak staves (Quercus sessiliflora Salisb.), with three industrial
scale replicates. Sampling was carried out after 30, 60, and 90 days of aging, and the wines were evaluated in terms of general
analysis, phenolic composition, total polysaccharides, multielement composition, and Sr IR. Li, Be, Mg, Al, Sc, Ti, V, Mn, Co, Ni,
Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Mo, Sb, Cs, Ba, Pr, Nd, Sm, Eu, Dy, Ho, Er, Yb, Lu, Tl, and Pb elements and 87Sr/86Sr were
determined by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and Na, K, Ca, and Fe by flame atomic
absorption spectrometry (FAAS). Two-way ANOVA was applied to assess wood aging and time effect on Sr IR and mineral
composition. Wood aging resulted in significantly higher concentrations of Mg, V, Co, Ni, and Sr. At the end of the aging period,
wine exhibited statistically identical Sr IR compared to control. Study suggests that wood aging does not affect 87Sr/86Sr, not
precluding the use of this parameter for wine traceability purposesinfo:eu-repo/semantics/publishedVersio
Neutrinos and the matter-antimatter asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero
neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny
constitutes a puzzling problem in particle physics. From the theoretical
viewpoint, the smallness of neutrino masses can be elegantly explained through
the seesaw mechanism. Another challenging issue for particle physics and
cosmology is the explanation of the matter-antimatter asymmetry observed in
Nature. Among the viable mechanisms, leptogenesis is a simple and
well-motivated framework. In this talk we briefly review these aspects, making
emphasis on the possibility of linking neutrino physics to the cosmological
baryon asymmetry originated from leptogenesis.Comment: 8 pages, 1 table, 1 figure; Based on talk given at the Symposium
STARS2011, 1 - 4 May 2011, Havana, Cuba; to be published in the Proceeding
Tabletop and Full-Scale Emergency Exercises for General Aviation, Non-Hub, and Small Hub Airports
ACRP Synthesis 72: Tabletop and Full-Scale Emergency Exercises for General Aviation, Non-Hub, and Small Hub Airports provides small airports with the tools and practices needed to practice emergency response. The report provides sample exercise tools and plans, a checklist of effective practices for tabletop and full-scale emergency exercises, and a road map for developing an effective exercise program
Emergency Communications Planning for Airports
TRB\u27s Airport Cooperative Research Program (ACRP) Synthesis 73: Emergency Communications Planning for Airports explores emergency communications planning and is specifically designed for use by airport senior management, public information officers, and first responders and emergency managers. The report includes sample communication plan tables of contents, field operations guides, and a checklist of effective communications plans
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